Andrey Rublev cut open his knee, after hitting himself six times with his racquet, during a burst of on-court frustration, against Carlos Alcaraz during their ATP Finals clash.
After being overturned 7-5 in the opening set, the Russian world No 5 cut an increasingly pent-up figure as he crashed his racquet into the court after missing a shot to hand Alcaraz break point in the first game of the second.
Missing the ensuing shot and being broken by the Wimbledon champion, the 26-year-old chose to punish himself, bringing the racquet down again and again until his kneecap was bloodied.
An emotional Rublev was then tended to by members of his team during the break between games, and continued play with the wound continuing to weep.
Upon Rublev's unraveling, Alcaraz - who had been matched well in the first set until his final break of serve - could waltz away with the victory in their first career meeting in straight sets, 7-5, 6-2.
When asked about his knee injury after Wednesday's match, Rublev was reticent when he pronounced it 'okay', adding: 'Nothing. Nothing happened.
But in the press conference after his defeat, the Russian expressed his disappointment with his form at the end of the season.
The tie is Rublev's second in Turin and their second defeat after losing to his compatriot and close friend Daniil Medvedev 6-4 6-2 in his tournament opener.
'It's not easy to take these defeats because I wanted to finish the season well,' Rublev said. 'Sometimes, when things don't work out, it's inevitable to be disappointed and today, I didn't know how to handle it.
'No matter who I face, I never want to lose, especially since the season is over and I haven't been able to show the best of myself in this tournament.
'It's very disappointing that I could not manage my frustration better,' the player added.
Two losses on the trot leave the player languishing last in his red group, behind Alcaraz in the lead, Medvedev, and Alexander Zverev, who Rublev will face in his final round-robin tie.
Before heading into the competition, Rublev was knocked out of the Paris Masters by eventual champion Novak Djokovic.
But the world No 1 has had a surprise start to the tournament in Turin - in his green group, Jannik Sinner leads the pack after defeating Djokovic for the first time in their head-to-head history.
The Italian was made to work for his victory against the US Open champion but went the distance to claim the 7-5 6-7 (5-7) 7-6 (7-2) win in just over three hours.